My Maternal Grandmother smoked around two packs of cigarettes a day for most of her life.
But when she turned 80, she decided to quit.
She was living with my Mother by that time so my Mother was happy about her decision.

Fast foward 12 years...
At age 92, she decided to start smoking again.
My Mother had her down to the doctor for a check-up one day and expressed concerns to him about her smoking again.
He said what are you going to do? Tell her smoking will kill her? She's 92, let her enjoy her cigarettes.

She passed away a little over two years after that at age 94 of an eschemic bowel.
Something totally unrelated to smoking.